Plants produce many small molecules with specific and potent biological activity. These are commonly economically important, either because they are valuable commercial products, or because they have regulatory functions as plant hormones or intracellular messengers. The genetic regulation of the synthesis of such compounds is often unknown. For example only a small fraction of the Arabidopsis genome is recognized as being involved in plant secondary metabolism. The problems in elucidating these pathways include low accumulation levels, transient or tissue-specific expression, or the complications associated with long multi-step pathways. To overcome these problems a strategy has been devised combining activation tagging mutagenesis (ATM) with pharmacological high throughput screening (HTS). In this, ATM of Nicotiana tabacum protoplasts are used to produce a mutant population of microcallus cultures, and individual clones that over-accumulate products with a specific biological activity are then selected after HTS. These mutant clones are then used to isolate the tagged genes responsible for this accumulation. This enables product-relevant genes to be identified without the requirement for understanding the metabolic pathway. However, because of the random nature of ATM, and the large genome size, as many as 300,000 individual mutants would need to be screened to cover the entire genome. Thus, there is a need for systems and methods to significantly increase screening throughput.